Add dual MIT/Apache-2.0 license files and a crates.io README. Bump dependencies to current: rand 0.8->0.10, aes-gcm 0.10->0.11, base64 0.22->0.23. Add keywords, categories, readme, rust-version fields to Cargo.toml. Migrate encryption.rs and test_vectors.rs to the new rand/aes-gcm/base64 APIs.